P0303: Cylinder #3 Misfire

How do I fix trouble code P0303? It's a simple enough question. Unfortunately, as with many error codes, there might not be a simple solution. We here at AutoZone understand the importance of having a fully functional vehicle, and we also know that these pesky error codes can create a level of frustration and stress. Therefore, to help you work through your anxiety, let's examine the P0303 error code and what that might mean for your vehicle and your pocketbook.

What Does P0303 Mean?

The first question you are likely asking yourself is, “what does the code P0303 mean?” This code is a generic error message that relates to OBD-II equipped vehicles, and it refers to issues in the powertrain. However, the code does not necessarily refer to any specific actions that should be taken as these steps will vary based on the make and model of your vehicle. However, the code does indicate that the vehicle’s computer system has sensed an issue in at least one of the car’s cylinders. In this specific case of error code P0303, the computer system is notifying the driver the cylinder number three is not firing as it should.

What Causes P0303?

While it is always beneficial when a problem’s cause is evident and easy to resolve, this specific error code can be caused by a number of factors, spanning from affordable to expensive. For example, the issue can stem from a faulty spark plug or wire, which in the grand scheme of things is relatively easy to repair. However, the error code may also occur because of a faulty catalytic converter or defective computer system, which can vary in expense. Although there are several other possibilities as well.

  • Faulty coil 
  • Faulty fuel injector
  • Faulty oxygen sensor
  • Poor compression 
  • Burned exhaust valve
  • Low or no Fuel

What are the Signs of P0303?

While everything is clearer in retrospect, it still pays to understand the potential warning signs of this particular problem. For example, if your engine seems to be harder to start, or if it seems to stumble or hesitate upon ignition, then it could be a sign that one of your cylinders is not acting the way that it should. However, pinpointing the specific cylinder can be a complicated process without the assistance of the error code message. Therefore, if you experience such issues without an error code, then you might be best served by taking your vehicle in for a diagnostic test.

How to Fix P0303

While some elements of the possible resolutions for error code P0303 might require an experienced mechanic, some issues might be resolved by a novice mechanic or DIYer.

For example, if you are experiencing hesitating or stumbling of the engine in addition to the error code, then the problem is likely related to the spark plugs or wiring. Therefore, check that the connectors and wiring leading to the problem cylinder are secure and in good condition. However, depending on the age of the car, it might be beneficial to change out these ignition components as part of routine maintenance. If the wiring and spark plugs appear to be in good working order, then you can check the coil packs for any signs of wear. Also, the catalytic converter may have gone bad. A clear indication that this is the case is if the exhaust smells like rotten eggs. Last, the issue might stem from faulty fuel injectors.

Before trying your hand at any of these replacements, it is best to do an honest assessment of your skills because you do not want to do any further damage to your vehicle. Although, in some instances, the computer malfunctioned and merely needs to be reset.

The OBD-II scanner error code P0303 problem can be frustrating. However, if you have patience and the skills necessary, you can root out the cause, and have your car back to its full potential. You can get the parts you need at your local AutoZone Store. If the job is too big for you, seek out one of our Preferred Shops to help you do the job.

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